1. Technical Field of the Invention
The present invention relates to a band division apparatus that is especially suitable for use in an electronic musical instrument or the like that requires high sound quality.
2. Description of the Related Art
A so-called multi-amp system is used for electronic musical instruments or other acoustic devices, especially for those which require high sound quality. When the multi-amp system is used, a musical sound signal is divided into signals of different bands. The signals of the different bands are amplified through respective amplifiers and the amplified signals are then emitted through respective speakers of the bands.
Example filtering characteristics of filters used for band division are described as follows with reference to FIG. 4 which is also used for a later description of an embodiment of the invention. As shown in FIG. 4, a musical sound signal is divided into signals of three bands, i.e., low, intermediate, and high bands, and the low and intermediate bands cross over at a crossover frequency f1, and the intermediate and high bands cross over at a crossover frequency f2. In this example, the filtering characteristics of the filters are adjusted such that the sum of gains of the filters is about “0 dB” at any frequency included in the bands of the musical sound signal.
Since the musical sound signal is first generated as a digital signal and is then converted into an analog signal through a DA converter, either an “analog stage” or a “digital stage” is conventionally selected as a band division location at which the musical sound signal is divided into bands. In the case where the “analog stage” is selected as the band division location, first, a digital signal is converted into an analog signal through one DA converter and the analog signal is then divided into bands, for example, through a channel divider described in Non-Patent Reference 1.
On the other hand, in the case where the “digital stage” is selected as the band division location, first, a digital signal is divided into bands, for example, through a digital filter and respective analog signals of the bands are then obtained through the same number of DA converters as the number of the bands. Accordingly, 3 DA converters are required when a musical sound signal is divided into three bands as shown in FIG. 4. A technology for band division at the digital stage in this manner is described, for example, in Patent Reference 1.
[Patent Reference 1] Japanese Patent Application Publication No. Heisei 6-54395
[Non-Patent Reference 1] “F1030 Manual”, Yamaha Corporation, 1976
However, each of the above technologies has the following problems.
First, in the case where a musical sound signal is divided into bands at the analog stage, to construct a channel divider, there is a need to use parts, which are highly accurate and also have high stability to temperature change or temporal change, or a complicated circuit scheme, which is disadvantageous in terms of cost. This is because it is necessary to set the sum of gains of signals of two adjacent bands at any frequency around the crossover frequency to about “0 dB” and also to synchronize the phases of the signals of the two adjacent bands.
On the other hand, the same number of DA converters as the number of the bands is required in the case where a musical sound signal is divided into bands at the digital stage. However, if the number of required DA converters is increased, cost is increased, especially in the case of electronic musical instruments or the like which require high sound quality since such electronic musical instruments also require high quality DA converters.